There is a high degree of uniformity in system configurations for desktop computer systems. Most desktop computers have one or more hard drives, an external monitor, a CDROM drive, and a floppy drive. This general system configuration is consistent within the product lines of vendors and across different vendors.
Uniformity in system configurations, however, does not exist in portable computers. It is not uncommon for a given vendor to offer portable computers that provide varying levels of portability. Some larger models will have all of the capabilities of desktop models, and will consequently be larger. In parallel, the vendor will also offer more streamlined models where features are sacrificed to augment portability. These computers will have one or no removable disk drives, small battery packs, and heightened low-power capabilities.
Especially in the smaller, more-portable end of the spectrum, the portable computer system designer becomes extremely sensitive to the system size versus capability tradeoff. To make the systems smaller, many times the size of the battery pack is reduced as are the number of bays for peripheral devices.
One part of the portable computer, however, can be optimized without any concomitant loss in system capability. This is the portable computer's enclosure. Space within it can be used more effectively and structural features of the system can be shared between various components to yield a system that has no loss in toughness yet is smaller and lighter.